Water Rocket Forum

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A water rocket is a type of model rocket using water as its reaction mass. The pressure vessel (the engine of the rocket) is constructed from thin plastic or other non metallic materials (usually a used plastic soft drink bottle) weighing 1,500 grams or less. The water is forced out by compressed air. It is an example of Newton's third law of motion.

Except for the class D competition, most of the competition records are achievable only by organizations having access to advanced manufacturing techniques or processes (such as carbon-fiber filament winding machines). As I mentioned in this post in another thread, this presents kind of a disincentive to compete.

So I propose a re-organization of the competitions, in which each class would have two or three subcategories:

Class A would still be single-stage, and the current record would fall under the "open" category. The current class D record would fall under the proposed class A "unmodified soda bottle" category. And a new category would be available for the soda bottle enthusiasts to experiment with splicing.

Class B would include the same subcategories, with the current record falling under the "open" category. New categories would be available for soda bottle enthusiasts to compete with single-bottle stage designs and spliced bottle staging designs. Detachable boosters would also fall under class B.

Class C - I'm not sure what this is for. It seems that the winner here would be the highest-altitude rocket with the largest parachute? Since parachutes are nearly negligible in weight when made from plastic film, it seems that the current class A record holder with a large parachute would beat the record under the class C rules. In any case, if we have a duration record, the same three sub-categories would still apply.

Class D would be folded into the new class A unmodified soda bottle category. Or, if kept as its own class, we could leave class A alone and instead have two unreinforced bottle categories in class D: single bottle and spliced bottle.

Class E - there have been no takers for this competition, and in my previous post in that competition thread I explained why I think that's the case. I feel that this class could be eliminated or folded into an additional category in the proposed new class A.

Water rocket dragster (by the way, the standing page misspells this as "Dargster") - currently the rules are written as an "open" competition where anything goes with respect to pressure vessels. This competition would also benefit from having categories that include unreinforced single and spliced bottles.

My objective in this reorganization is to open up competitions to people or teams who don't have access to advanced composite manufacturing processes, who would rather use soda bottles. Another thing to consider would be a category for using other off-the-shelf parts such as fluorescent tube sleeves.

Been giving your suggestions a second thought.

I think you may be right about certain competitions having a "hard limit" that once achieved, no one will be able to do better and that might be discouraging participation. (especially the competitions where pressure is limited or the bottle cannot be modified. After all how high can an unmodified 2 liter bottle go when the pressure is also limited.

I propose that the classes be reorganized as follows.

1. Class A & B will remain unchanged.

2. Class C (flight duration) will be removed (it was a great low cost competition back in the days when onboard cameras and altimeters were expensive) but the participant would probably need an extremely large launching area to account for drift which may be impractical for some teams.

3. The water rocket car competitions remain unchanged and will be called Class C (water rocket dragster).

4. Class E (reinforced bottle will be removed (competitors going through the trouble and expense of reinforcing a bottle will most likely enter it in the A or B competitions).

5. This is where the most changes will take place So start the suggestions rolling. The unreinforvced bottle competition. It should be opened up to sliced rockets and have no pressure limits (the fact that the bottles will not be reinforced will "self police" the pressure limits yest keep the pressures in a range that special equipment (high pressure compressors, scuba tanks, etc. will not be needed. This also eliminates the need for accurate pressure gauges as well. Teams can splice, couple or whatever (as long as the bottles are not reinforced. we will probably need a way to prevent "painted" rockets being used to disguise reinforcements. (maybe a requirement that a specific amount of the rocket be "clear". Weight limits and general requirements will be the same as the class A and B (camera onboard, altimeter, 2 flights etc.).

6. Make a unreinforced multi stage class ( the new class E) with similar construction requirements listed above in the unreinforced bottle competitions.

Lisa Walker,Forum Administrator. The Water Rocket Achievement World Record Association

I think you may be right about certain competitions having a "hard limit" that once achieved, no one will be able to do better and that might be discouraging participation. (especially the competitions where pressure is limited or the bottle cannot be modified. After all how high can an unmodified 2 liter bottle go when the pressure is also limited.

Actually that's part of the fun of the challenge. For safety I advocate retaining a limit on pressure, and require accurate pressure gauges (they are cheap, a fraction of the cost of an altimeter). The theoretical limit for a 2-liter water rocket is way higher than the records achieved so far. A 2-liter soda bottle at 100 psi and a 2-liter FTC rocket at 100 psi will have dramatically different altitudes. As the recent class D record just proved, careful attention to rocket design can have great results. I've got a new design of my own that my calculations predict will beat the current record by nearly 10 meters.

I have mixed feelings about eliminating the duration contest. On one hand, I felt the duration winner could simply be the class D winner with a bigger parachute, so it seemed to be a pointless contest. On the other hand.... I've been toying with concepts for a swing-wing glider as an alternative to a parachute (at apogee, the wings deploy and the rocket glides down - properly designed, it could even be radio-controlled so it doesn't get lost). But overall I have no problem with eliminating that one for the reason you stated: you need to have a very wide open space available.

5. This is where the most changes will take place So start the suggestions rolling. The unreinforvced bottle competition. It should be opened up to sliced rockets and have no pressure limits (the fact that the bottles will not be reinforced will "self police" the pressure limits yest keep the pressures in a range that special equipment (high pressure compressors, scuba tanks, etc. will not be needed. This also eliminates the need for accurate pressure gauges as well.

Another objection I have to this is that it effectively invalidates previous records. Limiting the pressure presents an interesting challenge and levels the playing field, so that the ROCKET is what wins the contest, and not its internal pressure.

I see in your draft you have retained the 100psi limit in section I.1.

I'd like to see that limit remain. Safety is still a concern, and bottles these days seem thinner than those of years ago. Granted, you have 50 feet of hose, but if your kid chases a cat that wanders near a rocket pumped almost to bursting and it explodes, that's bad. A 2 liter bottle can withstand about 150psi. 20% margin is reasonable for safety, so 120psi would be a reasonable max pressure. But many pressure gauges go up to only 100psi, so 100psi is a reasonable pressure to keep the playing field level.

I would like to see section IV.2 expanded to include separate and distinct contests, rather than lumping all variations of rockets into one class.

I suggest keeping the current class D rules for single unreinforced bottles, limited to 100psi with an accurate gauge. Call it class D1. I see no reason to replace a long-standing contest that has had a lot of participation already.

We can have another category, say D2, for spliced bottles. And maybe D3 for FTC rockets? (I recently saw tube covers at Home Depot, so I know they're still available). That would open up the competition to a lot of inventiveness, I think. And the pressure can be unlimited for those categories.

I'm nervous about removing pressure limits for spliced bottles. In my experience the splice is the weak point. Maybe I did it wrong the one time I tried it, who knows. In my case the failure wasn't catastrophic, it simply sprung a leak and I had to throw away the rocket. Limiting pressure here isn't so much a safety concern rather than a means to preserve your work!

We will probably need a way to prevent "painted" rockets being used to disguise reinforcements. (maybe a requirement that a specific amount of the rocket be "clear". Weight limits and general requirements will be the same as the class A and B (camera onboard, altimeter, 2 flights etc.).

Well... painting has a weight penalty. Even electrical tape is pretty heavy, useful as it is. But I agree the rocket body should not be wrapped by anything. Requiring the rocket be "clear" won't work; it invites cheating by wrapping with clear packing tape. How about requiring that the skin of the pressure vessel serve as the outer surface of the rocket body?

6. Make a unreinforced multi stage class ( the new class E) with similar construction requirements listed above in the unreinforced bottle competitions.

Another thing just came to mind, about keeping the playing field level. And this may needlessly complicate things but maybe it should be accounted for.

I've probably written the only water rocket simulator (that I know of) to account for atmospheric conditions: temperature, barometric pressure, and relative humidity. And I am seeing that these have an amazingly significant effect on rocket performance. For a 2 liter bottle at 100 psi, the difference between a hot humid day and a cold dry day can be 10 meters (33 feet) of altitude!

Hot humid days are best for water rockets, because the air is less dense, reducing drag. Such days are available where I live, but folks in colder climates may not have such opportunities. So in effect their rocket is getting penalized by their atmospheric conditions.

If each contestant would record the conditions at the time of launch, the rocket's performance could be adjusted for some set of "standard" conditions, like 72°F at 29.92 inches of mercury and 25% relative humidity. Then we'd have a means to make apples-to-apples comparisons between launches.

This is easy to do... the Weather Underground monitors thousands of commercial and home weather stations around the world. Here's the one nearest to the field I last used for launching (and won't use again due to interference from radio-controlled aircraft: https://www.wunderground.com/personal-w ... CALOSAL161
People could simply look up conditions near to their launch time and record them.

Having weather conditions would help compare a rocket launched in, say, the United Kingdom against a rocket launched in Florida.

Maybe you are right about leaving the duration competition in place due to past records achieved and the fact that someone might make a glider. Maybe a better idea would be to change that competition into a glider competition. That would inspire some innovation in an area of water rocketry that has not been extensively explored.

For the unreinforced bottle competition I have mixed feelings on pressure limits. With a fixed pressure limit, the competition turns into a "weight reduction/aero competition with a theoretical "hard ceiling" that cannot ever be overcome. I kind of like the idea that someone can push the limits of pressure. By limiting the materials to plastic containers (including FTC tubes), the pressure limit would still be reachable inexpensively. This also eliminates the need for an accurate measuring device. I kind of envision an "anything goes class (using plastic containers, not reinforced, in any configuration (one stage, 2 stage, side boosters, FTC, etc. This might inspire more competition while keeping costs down to where the biggest checkbook doesn't always win.

As for sub categories, see above. When the WRA2 was formed records were constantly in dispute with numerous people claiming records in self designed "sub classes" which met their particular design. Even after the association was formed in those early days, we had issues with "self proclaimed" records.

I would like to see this new class have a high participation rate with rival teams trying to beat one another using different designs. Maybe someone comes up with a reliable lightweight staging mechanism going up against a FTC rocket and someone else finds a container that holds more pressure going against them both.

Lisa Walker,Forum Administrator. The Water Rocket Achievement World Record Association

If the duration competition is kept, it can be kept open, not restricted to gliders. Parafoils are another possibility, since they also provide lift (not just falling resistance) and can potentially increase duration.

As to pressure... I guess safety is managed well enough by requiring 50 feet of pressure hose. OK, yes, you've convinced me that removing pressure limitation makes it interesting.

I still like having a stand-alone class for a single unreinforced bottle, even with no pressure limit. The current winner is active here, and he can easily re-establish his class D record with higher pressure. But please, let's keep that single-bottle class pure. If there are no sub-categories, then let's have a separate "unreinforced open" class in which anything goes (staging, splicing, drop-off boosters, multiple bottles, FTC, etc).

I believe there will continue to be a strong interest in creating the best-performing rocket that's also the simplest, without the complications of splicing and staging. So I suggest keeping class D as it is (but remove the pressure limit) and create a new anything-goes open unreinforced class.

I think the best option will be to replace the "reinforced bottle" (class E) with this new "unreinforced plastic container" class (will have to come up with a catchy name). There are no records set in that class and as was mentioned earlier, the competitors entering would probably skip over it and go directly to compete in the A or B classes.

The unreinforced bottle should remain the same with maybe an additional requirement of an calibrated pressure measurement.

For the flight duration, there should be some promotion to use gliders or some kind of glider challenge to encourage development in the community.

We should not forbid the use of tape or even paint on the rockets as it could be used for decorative purpose or even to make the rocket easier to find but the tape should not be used in a way that structurally reinforces the pressure chamber. A lot of teams use the tape to attach payload bays enclosing or attaching cameras and altimeters or even fins.
Making a rule requiring that the skin of the pressure vessel serve as the outer surface of the rocket body will also not work as a pure composite rocket would meet that criteria too.

Clear packing tape does not handle being wet very well and so it is not a good choice for reinforcement.

Lisa Walker,Forum Administrator. The Water Rocket Achievement World Record Association

Sounds good to me. How about "Unreinforced plastic pressure vessel" for class E? I can see someone making a rocket out of PVC pipe. The challenge with that might be keeping the weight under 1.5 kg.

Keeping class D the same but adding a calibrated pressure measurement wouldn't affect the current record, because he posted calibration info after the submission, so that's fine too.

For flight duration, maybe just a tweak in the existing rules to mention that methods to achieve gliding flight as well as slowed vertical descent are acceptable.

As for tape, yes I agree. I'm just saying that if I wrap a bottle in clear packing tape, it might serve to reinforce the bottle. The outside of my rocket doesn't get wet, so wetness isn't an issue. I never tried it. I just brought it up to suggest that visual transparency may not be a good way to assess whether a bottle is unreinforced.

Making a rule requiring that the skin of the pressure vessel serve as the outer surface of the rocket body will also not work as a pure composite rocket would meet that criteria too.

Not if the rules required also that the pressure vessel be available off-the-shelf (like soda bottles or FTC covers) and be made from a homogeneous plastic material (which would eliminate composites).

I will share some of my thoughts on class D. Changing the rules for class D would be a mistake. Class D is what we all thought a soda bottle rocket was when we started. Heck, it's right there on the WRA2 logo. The class D framework is the best way to challenge builders using the fewest resources. Changing the pressure limit will remove many options in construction and narrows the safety margin in launch equipment. I have seen many scary launchers serving well because of the pressure limit. In my opinion, under the current rules class D record could be pushed to 600ft or more. I am working on Val5 now and will make a 500+ft record attempt in the spring. The need for an "open" unreinforced class is obvious. So much innovation is happening around the multiple bottle concept; it could be the most exciting class of all. Anything goes, as long as the rules of unreinforced construction are followed. The skill level necessary for successful splicing and more advanced launcher construction will make removing the pressure limit more realistic.

I will share some of my thoughts on class D. Changing the rules for class D would be a mistake. Class D is the first idea we all had when we started building soda bottle rockets. Heck, the single bottle concept is right there on the WRA2 logo. Class D is the best framework to challenge builders using the fewest resources including money. Changing the pressure limit will remove many options in pressure vessels and launchers for the beginner. In my opinion, class D with the current rules could be pushed to 600ft or more. I am currently working on Val5 for a 500+ft record attempt in the spring. The need for an “open” unrenforced class is obvious. The innovation I have seen around the multiple bottle concept could make it the most exciting class of all. Anything goes as long as the rules for unreinforced construction are followed. With the skill level needed for successful splicing and advanced launcher construction, the removal of the pressure limit would be more realistic. A truley open class will lead to far more diversity in design as well. When using a single bottle it will always boil down to efficiency, weight and environment no matter what pressure is used. But the complexity of something that seems so simple is a challenge I do enjoy.

I will share some of my thoughts on class D. Changing the rules for class D would be a mistake. Class D is the first idea we all had when we started building soda bottle rockets. Heck, the single bottle concept is right there on the WRA2 logo. Class D is the best framework to challenge builders using the fewest resources including money. Changing the pressure limit will remove many options in pressure vessels and launchers for the beginner. In my opinion, class D with the current rules could be pushed to 600ft or more. I am currently working on Val5 for a 500+ft record attempt in the spring. The need for an “open” unrenforced class is obvious. The innovation I have seen around the multiple bottle concept could make it the most exciting class of all. Anything goes as long as the rules for unreinforced construction are followed. With the skill level needed for successful splicing and advanced launcher construction, the removal of the pressure limit would be more realistic. A truley open class will lead to far more diversity in design as well. When using a single bottle it will always boil down to efficiency, weight and environment no matter what pressure is used. But the complexity of something that seems so simple is a challenge I do enjoy.

The text for the pressure limit has been removed from the new class draft. This class will replace the class E (reinforced bottle) class which has had no participation.

The goal will be to allow any style of rocket, any volume, single or multiple stage, with no pressure limit, provided that the 1500 gram weight limit and that the pressure vessel be constructed from plastic "containers" and is not reinforced using other materials. Spliced rockets will be allowed (although some clever competitor may attempt to "overlap" their "splices" 100% and create a double wall rocket) Something might need to prevent that method of reinforcement.

Does anyone else have any suggestions?

Lisa Walker,Forum Administrator. The Water Rocket Achievement World Record Association

As for class D, I still want to see the requirement of using a calibrated pressure gauge. This levels the playing field. A good pressure gauge isn't expensive compared to an altimeter. Many pressure gauges have published accuracy, for example a 3/2/3% gauge can be 3% off at the ends of its range and 2% off in the middle. Even 4/3/4% would be acceptable, way better than the 20% I've seen for built-in tire pump gauges. For exmple, here's a 3/2/3% gauge to 200psi for less than $4, free shipping for Amazon prime members. I'd recommend that a compention gauge be accurate to 3% or better at 100psi.

I have two pumps with built-in guauges. Compared to a calibrated gauge, one reads 20% too high and one reads 20% too low. So if I relied on either gauge, I would be penalizing myself or giving myself an unfair advantage. By my calculations, that 40psi difference between my two gauges would result in a variation of over 30 meters (100 feet) in apogee!

Plan right now is to finalize this draft by the end of the week and put it up for a vote during the beginning of December with the competition officially beginning on the 1st of January 2018. This class will replace the "Reinforced bottle" (Class E) competition and be open to unreinforced rockets of any design.

There will also be a separate issue to vote on to add a requirement for a 1% accuracy pressure gauge in competitions which have pressure limits. Wording will be added to those classes requiring a pressure gauge with a 1% accuracy be used and that the make and model of said gauge be presented in the record submission.

Comments and suggestions welcome.

Lisa Walker,Forum Administrator. The Water Rocket Achievement World Record Association

Two errors in IV.6: "Rocket must be transparent over at leats 50% of it's surface" -- "leats" should be "least" and "it's" shouldn't have an apostrophe here.

III.4 seems redundant in that IV.7 covers it already, but I'd leave them both in for safety.

As for pressure gauges in a different vote, 1% accuracy is somewhat expensive; I was lucky to find a good deal on mu 1% gauge. Inexpensive gauges at 3% accuracy are easier to find. Any published accuracy rating is better than none at all, and "none at all" is what one gets from built-in tire pump gauges.